1. Field of the Invention
The present invention relates to a digital electronic still camera for recording image data representing a still picture obtained by imaging in a memory card which is loaded in the camera so as to be freely loadable/unloadable.
2. Description of the Related Art
Analog electronic still cameras formerly were extensively used. At the present time, however, digital electronic still cameras are dominant. The analog electronic still camera has a solid-state electronic imaging device and subjects a video signal representing an image of a subject which is output from the imaging device to recording processing including modulation and then, recording the same in a recording medium (for example, a magnetic floppy disk) in the form of an analog signal. On the other hand, the digital electronic still camera converts an analog video signal into digital image data and records the same in a semiconductor memory contained in a memory card.
It is considered that factors which cause the digital electronic still camera to be widely used are that the camera can be made compact because the need for a rotating mechanism of a floppy disk and a transfer mechanism of a read/write head as in the analog electronic still camera is eliminated, and a memory card capable of storing large-capacity data and miniaturized is easily available. However, another important feature should not be overlooked. This feature is that an image (a picture representing a subject) can be handled by a so-called personal computer (PC) because the image is digitized (represented by digital data).
Digital image data stored in the memory card can be accepted in a personal computer to display an image on a display device connected to the personal computer. The image data accepted in the personal computer can be subjected to various types of image processing (for example, cutting of a partial image, synthesis of two or more images, and enlargement or reduction, emphasis or gradation of an image).
In order that image data representing as many frames (pictures) as possible can be stored in the memory card, image data compression processing is generally performed in the digital electronic still camera. The data compression processing makes it possible to reduce the amount of image data representing one frame.
One coding system of color still image data is a JPEG (Joint Photographic Coding Experts Group) system. An image data compression/expansion algorithm used in the JPEG system is the ADCT (Adaptive Discrete Cosine Transform) algorithm. The JPEG system is widely used in the computer industry, and is supported by a lot of types of personal computers manufactured by a lot of corporations. This ADCT algorithm is also applied to data compression/expansion processing in the digital electronic still camera. Consequently, compressed image data obtained by imaging and subjected to data compression and then, recorded in the memory card in the digital electronic still camera can be accepted in the personal computer, subjected to reproduction or other processing or stored in a file without using a reproducing apparatus dedicated to the memory card.
It is impossible to avoid slight degradation of the image quality by data compression of image data. In applications requiring high image quality, therefore, it is desirable that original image data is directly recorded in the memory card without being subjected to compression processing.
In the JPEG system, the Lothless mode in which all information included in original image data are recorded (one in which the difference between the original image data and compressed image data is written in addition to the compressed image data) is prepared. Unfortunately, an image data recording system under the Lothless mode is special and is not supported by personal computers commercially available. Image data recorded in the memory card in this system cannot be generally handled by the personal computers.